Flexible metal pipes with a shrinkable polymer sheath, a process for their fabrication, and their utilization as flexible tubular conduits

ABSTRACT

This invention relates to a flexible metal pipe covered with an impermeable sheath of a shrinkable, preferably semicrystalline polymer or polymers, characterized in that it incorporates between the shrinkable polymer sheath and the metal pipe an intermediate elastomer layer (8), optionally vulcanized or reticulated, and/or a TPE in the form of a continuous tubular sleeve (FIG. 3) or of a tape (FIG. 4 to 6). Sheathed pipes of this type are particularly suitable for flexible pipelines, optionally with suitable supports, for carrying oil and gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/120,621, which was filed on Sep. 10, 1993, now abandoned.

FIELD OF THE INVENTION

This invention relates to flexible metal pipes provided with ashrinkable polymer sheath, and in particular to flexible tubularconduits incorporating such a sheathed flexible metal pipe and offeringsignificant mechanical resistance especially to internal pressure,permitting their use for instance in off-shore oil and gas production.

BACKGROUND OF THE INVENTION

The flexible metal pipes may be produced in conventional fashion by thecoiling of a profiled interlocking strip (for example as per FR 2 555920) or of a wire with interconnected helical turns (for example as perFR 2 650 652) or by any other process that gives the pipe goodflexibility.

Flexible tubular conduits generally incorporate a flexible metal pipeserving as the inner frame which is formed by a helically coiled,profiled metal strip, for instance with inter-locking turns, whichinterlocking strip-coil frame is covered with an impervious polymersheath and the entire assembly is covered with reinforcing layers towithstand pressure as well as the underwater environment. Such flexibleconduits are described for instance in patents FR 2.619.193 and in"Recommended Practice for Flexible Pipe - API Recommended Practice 17 B(RP 17 B) First Edition Jun. 1, 1988".

Bending of the flexible metal pipes is made possible by providing spacesbetween the helical turns. The interconnection between the turns isnever impervious to liquids or to gas. Therefore, an impermeable polymersheath is fitted over the metal pipe. One may use for instancevulcanized rubber or, for conduits having greater mechanical strength, athermoplastic polymer offering the required mechanical properties, forexample polyethylene, for moving water or degassed crude oil in theextraction of underwater deposits.

What is most wanted, however, is to find a polymer material which offersthree qualities: Low permeability to liquids and/or gas, resistance to awide range of operating temperatures (both mechanical resistance andchemical insensitivity to high temperatures), and easy industrialimplementation. Certain semicrystalline polymers possess all of thesequalities, with the more crystalline types among them being ofparticular interest due to their low permeability. On the other hand,the higher the rate of crystallinity of a polymer, the higher its rateof physical stress as it passes from the molten state to itscrystallized solid state. If this shrinkage is prevented as in the caseof a sheath extruded around a metal pipe, residual stress is producedespecially in the form of tension within the polymer, weakening thesheath's shock resistance and flexibility.

Moreover, when the polymer sheath is extruded onto the metal pipe, thepolymer enters into the spaces between the helices, thus reducing thedegree of flexible movement of the pipe. Depending on the requiredproperties and the intended use of the flexible pipe, such interstitialpenetration of the polymer is acceptable in many cases. For certainapplications this penetration effect is even sought intentionally (FR 2268 614). However, given that high-resistance flexible conduits areenvisioned for heavy-duty operating conditions, it has been found thatthe penetration of the polymer in the spaces between the helices canhave a negative effect on the performance of the sheath. In particular,studies have revealed initial fissures which can lead to progressiveruptures and to leaks both locally and at the perimeter of the raisedsection of the sheath as a function of the degree of polymer penetrationbetween the helical turns.

For flexible pipes used in oil or gas extraction where the sheathmaterial must also stand up to live crude without blistering orinflating, the metal pipes can be sheathed with polyamide-11 (PA-11) or,for more demanding operating conditions, with a fluorinated polymer, inparticular polyvinylidene fluoride (PVDF). Polyvinylidene fluoride, byvirtue of its crystallinity, chemical near-insensitivity andimperviousness to liquids and gas as well as its resistance to atemperature on the order of 105° C. over many years, is the material ofchoice for the sheathing of flexible metal pipes, yet its rigidity doesnot permit such use.

To overcome this drawback, the PVDF may be plasticized. However,experience shows that the plasticizers migrate out of the polymer,causing the latter to return to its original rigidity over a period oftime depending again on the temperature of the liquids flowing throughthe pipe. One can also use plasticized PA-11 to produce a leak-proofpolymer sheath for flexible metal pipes. As an alternative to themodification of an excessively rigid polymer by the application oradmixture of a plasticizer, another known approach has been tocopolymerize a predominant part of the monomer corresponding to at leastone other comonomer.

Nevertheless, the polymer sheaths that can be produced by knownmethodology have limitations in their possible uses, the limitationsbeing dependent upon performance requirements, especially when the pipeis to carry live crude oil under high pressure and/or at hightemperatures. On the one hand, plasticized polymers are affected by themigration of the plasticizers and, in spite of the plasticizing, theyalso involve the risk of a weakening in the areas between the heliceswhen subjected to severe operating conditions. On the other hand,certain extra high-performance polymers whose use would be of interestwith no or relatively little plasticizing remain practically ineligibledue to their excessive rigidity.

SUMMARY OF THE INVENTION

It has now been found that it suffices to interposition an elastomerbetween the metal pipe and the shrinkable polymer.

This invention thus covers a flexible tubular conduit incorporating aninner flexible metal pipe whose outer surface displays interstitialspacings and which is covered by a shrinkable polymer sealing sheath,characterized in that it incorporates between the shrinkable polymersheath and the metal pipe an intermediate elastomer layer in a mannerthat the sealing sheath rests on the elastomer layer in the areas wherethe said sheath covers an interstitial space and that its penetration ofthe space is negligible or zero.

The prior art has not solved this problem satisfactorily. EP 166 385describes the wrapping of a polyester tape around the flexible metalpipe to prevent the PVDF from penetrating the spaces. That technique hasbeen tested and it has been found that the tape partially overlapsitself which is practically unavoidable in an industrial productionoperation and which proved to be enough to indent the PVDF and bringabout a rupture when bent.

U.S. Pat. No. 3,771,570 describes flexible metal pipes made up ofinterlocking helices and covered with a polymer sheath (preferably ofpolyvinyl chloride (PVC)). The problem posed was the shifting of thesheath relative to the metal pipe. An adhesive layer is thereforeincorporated between the metal helices and the PVC to make the PVCsheath adhere to the metal helices. The PVC completely penetrates thespaces between the helical turns.

GB 373 302 describes flexible conduits without reinforcing armor whichresist internal pressure, incorporating a flexible metal pipeconstituted of interlocking helices covered with a rubber sealingsheath, and a thin, relatively strong layer consisting for instance of asheet of cellophane sandwiched between the interlocking helices and therubber for the purpose of protecting the latter from the petroleumcarried by the flexible pipe. Between the metal helices and thecellophane sheet one can also insert a filler material. The cellophaneis in the form of a tape wrapped around the helices or applied as acoating in the form of a solution. The rubber is then applied to theoutside and vulcanized. The vulcanization serves to facilitate theadhesion and the penetration of the cellophane sheet which forms atroughlike fold in each space between two helical turns, with each suchspace corresponding to a very marked bulge on the inner surface of therubber. That is exactly the opposite of what is intended by this presentinvention.

According to the present invention, an elastomer is applied around theflexible metal pipe in an amount large enough to prevent the shrinkablepolymer from penetrating the spaces between the helices very much if atall, with the elastomer thus forming around the flexible metal pipe anintermediate layer which may envelop the pipe either in one piece or insections. The elastomer penetrates each individual space between thehelices either partly or entirely. Empirical investigation has shownthat, due in particular to the right choice of elastomer material, theshrinkage of the polymer sheath which took place upon cooling afterextrusion causes a portion of the elastomer to penetrate theinterstitial spaces and to substantially reduce or even eliminateessentially any residual stress on the polymer of the sealing sheath.

Also, the amount of elastomer already in place in the interstitialspaces at the time of the polymer extrusion can be selected, as afunction of the respective viscosity values of the elastomer and thepolymer of the extruded sheath, in a way as to prevent the formation ofsignificant bulges that are encountered in the fabrication of flexibleconduits along earlier techniques. It is also possible to limit thepenetration of the polymer sheath in the area where it covers aninterstitial space in such a way that the inner surface exhibits only aslight, not very high nor significantly curved enlargement. Inparticular, this inner surface can be essentially cylindrical with anearly constant cross section over the length of the flexible conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the cross-section along a longitudinal axis of a flexibletubular conduit according to the first mode of implementation of thisinvention.

FIG. 2 shows the cross-section along a transverse axis of a flexibletubular conduit according to the first mode of implementation of thisinvention.

FIG. 3 shows a longitudinal cross-section of a flexible tubular conduitintended for carrying water, oil, or gas in an offshore extractionoperation according to the first mode of implementation of thisinvention.

FIG. 4 shows an enlarged, partial longitudinal cross-section through aflexible conduit according to a second mode of implementation of thisinvention.

FIG. 5 shows an enlarged, partial longitudinal cross-section through aflexible conduit according to a second mode of implementation of thisinvention, detailing partial penetration by elastomer into theinterstitial spaces.

FIG. 6 shows an enlarged, partial longitudinal cross-section through aflexible conduit according to a second mode of implementation of thisinvention, detailing essentially complete penetration of theinterstitial spaces by elastomer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated above, the present invention provides an elastomer which isapplied around a flexible metal pipe in an amount large enough toprevent the shrinkable polymer from penetrating the spaces between thehelices very much if at all, with the elastomer thus forming around theflexible metal pipe an intermediate layer which may envelop the pipeeither in one piece or in sections.

The elastomer penetrates each individual space between the heliceseither partly or entirely. Empirical investigation has shown that, duein particular to the right choice of elastomer material, the shrinkageof the polymer sheath which took place upon cooling after extrusioncauses a portion of the elastomer to penetrate the interstitial spacesand to substantially reduce or even eliminate essentially any residualstress on the polymer of the sealing sheath.

Also, as indicated above, the amount of elastomer already in place inthe interstitial spaces at the time of the polymer extrusion can beselected, as a function of the respective viscosity values of theelastomer and the polymer of the extruded sheath, in a way as to preventthe formation of significant bulges that are encountered in thefabrication of flexible conduits along earlier techniques. It is alsopossible to limit the penetration of the polymer sheath in the areawhere it covers an interstitial space in such a way that the innersurface exhibits only a slight, not very high nor significantly curvedenlargement. In particular, this inner surface can be essentiallycylindrical with a nearly constant cross section over the length of theflexible conduit.

In a first implementation of this invention, the elastomer layerconstitutes a tubular sleeve covering the flexible metal pipe in onepiece. In the areas where it covers the cylindrical median section ofthe helices making up the flexible metal pipe it has a nearly constantthickness which is preferably between 0.1 and 2 min. The polymer sealingsheath does not touch the flexible metal pipe at any point.

In a second implementation, instead of covering the entire flexiblemetal pipe, the intermediate elastomer layer is placed only in theinterstitial spaces between the helical turns. In this design theelastomer layer is in the form of a more or less thick, continuous tapehaving an approximately constant cross section and being applied in agenerally helical fashion around the axis of the flexible conduitcorresponding to the free space between neighboring helical turns of theconstituent sections, such as interlocking helical strips, of theflexible metal pipe.

Alternatively, the elastomer layer may be comprised of two, three, oreven more helicoidal elements, for instance tapes, when the flexiblemetal pipe consists of two, three or more sections.

In the above implementations the elastomer fills the outer part of eachinterstitial space to a more or less significant depth, with theelastomer coverage of the free area within the spaces optionally beingessentially complete. Preferably, the amount of elastomer should bebetween 25% and 75% of the free spatial volume within the spaces betweenthe helices.

The shrinkable polymer

The shrinkable polymer is defined as any one polymer or mixture ofpolymers whose mold shrinkage is greater than or equal to 0.3%, 1% or,better yet, 3%. The shrinkable polymer is preferably of thesemicrystalline polymer type.

The semicrystalline polymers which are suitable for the purposes of thisinvention are those described in the POLYMER HANDBOOK, Third Edition(published by BRANDRUP and E. H. IMMERGUT) VI/1 to 89, and in particularthe following:

--the polyolefins,

--the polyamides.

--the polyurethanes and polyureas,

--the polyesters,

--the polyethers,

--the polyoxides,

--the polysulfides (PPS),

--the polyether-ether-ketones (PEEK) and their copolymers,

--the fluorous polymers such as:

--the homo- and copolymers of vinylidene fluoride (VF₂),

--the homo- and copolymers of trifluoroethylene (VF₃)

--the copolymers, and especially terpolymers, associating remainders ofthe activators chlorotrifluoroethylene (CTFE), tetrafluoroethylene(TFE), hexafluoropropene (HFP) and/or ethylene and optionally theactivators VF₂ and/or VF₃.

Among the fluorous polymers, the more suitable ones are the vinylidenefluoride-based homo- and copolymers due to their excellent chemicalinsensitivity to live crude oil or gas and their stability at hightemperatures. By way of example, especially for oil and natural gas, ithas been noted that a copolymer having at least 50% by weight vinylidenefluoride activators in the polymeric chain could provide sufficientimpermeability. The definition of fluorous polymers also refers tomixtures of at least 70% by weight of the above with other polymers.

Without departing from the substance of this invention, the shrinkableand preferably semicrystalline polymers may also contain plasticizers,fillers, pigments, stabilizers, anti-impact reinforcements, and othersuch conventional additives.

The elastomeric polymers The elastomeric polymers which make suitablematerials for producing the intermediate elastomer layer (8) are definedby ASTM D 883 as materials which, at ambient temperature, quickly returnto their approximate initial dimensions and shapes after havingundergone a significant deformation as a result of minor stress appliedto the slack material.

Suitable elastomeric polymers not only include elastomers proper(applied in their vulcanized or reticulated state) but alsothermoplastic elastomers (widely referred to as TPE) which exhibit anelongation at their flowage threshold of greater than 15%. The TPEs rankbetween thermoplastic resins which are easy to work with and versatilebut have limited temperature-resistance qualities or dynamic properties,and the elastomers having highly elastic properties but are difficult towork with, complex and often environmentally polluting. The structure ofTPEs always displays two incompatible phases one of which bringstogether the dispersed thermoplastic sequences in the elastomer phase.In general one distinguishes between 5 TPE categories:

--The thermoplastic polyolefin elastomers (TPO) are physical mixturesmade from polyolefins. There are those which contain more than 60%polypropylene and those with a preponderant elastomer phase (over 70%)and which may or may not be reticulated.

--The polystyrene-based copolymer units whose rigid phase consists ofpolystyrene sequences while their pliant phase may be formed forinstance by polybutadiene (SBS), polyisoprene (SIS), orpoly(ethylene/butylene) (SEBS) sequences.

--The polyurethane-based copolymer units (TPU) which can be obtained bythe joint reaction of a diol of high molecular mass constituting thecrystallizable pliant sequence of the TPE, with a diisocyanate and adiol of low molecular mass which engenders the rigid sequence.

--The polyester-based copolymer units such as those obtained by thecopolymerization of a polybutylene terephthalate (PBT) or a polyethyleneterephthalate (PET) which constitutes the rigid and crystallinesequences, and a glycol of low molecular weight (butane diol, diethyleneglycol) which, in association with a polyalkylene ether glycol, formsthe crystallizable pliant sequence.

--The polyamide-based copolymer units whose rigid sequences areconstituted of polyamide (PA) and the pliable crystallizable sequencesof polyether, also known as polyetheramides.

Preferably, the stiffness of the elastomer is less than that of theshrinkable polymer: It can be evaluated in terms of torsion and/orflexion and/or tension moduli and/or Shore hardness values which valuesare measured under the same conditions for both the elastomer and theshrinkable polymer. Preferably, the stiffness of the elastomer shouldremain below that of the shrinkable polymer regardless of the operatingconditions when in use, especially in terms of temperature and in dueconsideration of the ageing of these materials.

It is preferred that the elastomer be of a Shore A hardness at 23° C. ofless than 92 (and ideally less than 70), or of a Shore D hardness ofless than 50 when measured by the ISO 868 standard.

Preferably, the torsion modulus of the elastomer at 23° C. is less than100 N/mm² or, better yet, less than 30 N/mm² and ideally less than 10N/mm² (measured according to DIN standard 53447).

It is preferred that the tension modulus of the elastomer at 23° C. beless than 400 MPa or, better yet, less than 100 MPa (measured accordingto ISO 527).

Preferably, the tensile strength i.e. break elongation of the elastomerat 23° C. is greater than 50%.

In the case of TPEs, the preferred material is one which has a VICAT ofless than 70° C. when measured by the A/50 method according to the ISO306 standard.

It is best to use elastomers which simultaneously display theabove-specified values in terms of hardness, VICAT level, torsionmodulus and breaking elongation.

Preferably, the torsion modulus of the elastomer remains below 30 N/mm²(measured according to DIN standard 53447) over the course of itsthermal ageing.

The elastomers and/or TPEs specially recommended within the framework ofthis invention may be selected from among copolymers ofethylene/propylene/diene monomer (EPDM), acrylonitrile/butadiene/styrenecopolymers, methylmethacrylate/butadiene/styrene copolymers,ethylene/carbon monoxide copolymers, ethylene/carbon monoxide/vinylacetate terpolymers, acrylic rubbers, thermoplastic copolyethers/esters,polystyrene and polyisoprene, polybutadiene, and the like copolymersequences, styrene/butadiene/styrene copolymers, ethylene/ethylacrylate,ethylene/ethylacetate and ethylene/vinyl acetate copolymers as well astheir terpolymers, fluorous elastomers, silicone elastomers, fluoroussilicone elastomers, and polyurethanes.

Within the framework of this invention one can also use elastomer and/orTPE mixtures.

For the requirements of this invention one can use a thermoplasticpolyurethane (TPU) elastomer of a Shore A hardness less than 92 asmeasured in accordance with ISO standard 868. Moreover, it is preferredthat this elastomer can sustain a strong viscosity reduction duringthermal ageing. This viscosity reduction is preferably at least 60%after 30 days at 120° C. The thermoplastic polyurethane elastomerusually displays a viscosity at 20° C. that lies within the image shownbelow. The values take into account the RABINOWITCH correction asapplied to non-Newtonian liquids.

    ______________________________________                                        Corrected shear rate s.sup.-1                                                                 Viscosity in kPa.2                                            ______________________________________                                         4.09           0.7-1.3                                                       13.64           0.25-0.85                                                     36.15           0.19-0.78                                                     122.91          0.12-0.70                                                     ______________________________________                                    

The shear rate shown is also the shear-deformation rate gradient.

In general, the elastomer should preferably have a high level ofchemical insensitivity and temperature stability, especially in the caseof conduits carrying live crude which contains various components thatare highly damaging to a great many plastic materials. Especially in thecase of live crude which generally includes a more or less significantwater content, the elastomer chosen should preferably be one that is notsusceptible to the effect of hydrolysis on the relatively hightemperature of the crude coming out of the well, nor to any other formof water-induced degradation. Also, as a function on the one hand of theshrinkable polymer selected for the sealing sheath and, on the otherhand, of the operating environment of the conduit and in particular thetemperature and the liquids carried, the elastomer is preferably chosenin a way that any possible degradation products do not pose the risk ofaffecting the performance characteristics of the shrinkable polymer asthey progressively migrate through the sealing sheath.

An interesting example of elastomers possessing the desired propertiesof stability and chemical insensitivity is found in the silicone group,and in particular the elastomer silicones of the RTV type (vulcanizableat ambient temperature) or HCR type (cold-vulcanizable). In the case ofHCR as well as RTV silicones, the vulcanization can be performed incontinuous fashion so as to speed up the operation, with the flexibleconduit being drawn through or past heating devices (such as a hot-airor radiant or other type of heating system).

The elastomer is selected and applied in a way that its interpositionprevents the penetration of the polymer of the sheath into the recessesbetween the helical turns; thus, the flow of the hot material during theextrusion of the polymer sealing sheath and the effect of the stressapplied by the sheath during its shrinkage will cause it to penetratethe open spaces of the outer surface of the flexible metal pipecorresponding to the interstitial spaces between the helical turns in away that the polymer of the sheath is free to retighten itself aroundthe metal pipe without generating within itself any internal stress.

The drawings

FIGS. 1 and 2 of the attached diagrams show the cross sections alongboth axes of a flexible tubular conduit according to the first mode ofimplementation of this invention. The interlocking articulation lips(16,17) of the flexible metal pipe (2) create interstices and spaces (5)between the helical metal turns. The elastomer layer (8) covers themetal pipe, filling all the spaces between the metal helices. Thiselastomer layer serves as an intermediate layer between the flexiblemetal pipe and the outer, shrinkable polymer layer (9).

FIG. 3 of the attached diagrams shows the cross section of a flexibletubular conduit again according to the first mode of implementation ofthis invention but more specifically intended for carrying water, oil orgas in an offshore extraction operation. The flexible metal pipe (1)constituting the inner frame of the flexible pipe (2) is produced byclosely coiling an interlocking strip (3) whose successive turns (4a,4b, 4c, . . . ) delimit an interstitial space (5) that opens toward theoutside in a generally helical configuration, as well as internalinterstices (6) that open toward the inside of the pipe, and innerspaces (7) which are more or less closed. The elastomer layer (8) coversthe flexible metal pipe in continuous fashion, filling all theinterstitial spaces (5) between the helical turns. This elastomer layerserves as the intermediate layer between the flexible metal pipe and theshrinkable polymer layer (9) which constitutes the inner sealing sheathof the flexible conduit. The reinforcing armor cladding on the outsideof the sealing sheath assures mechanical strength of the flexibleconduit and in particular its resistance to internal pressure within thepipe when in use, the effect of the internal pressure being fullytransmitted to the said armor through the sealing sheath. The plasticmaterial of the sealing sheath is thus subjected to very specificworking conditions, with a virtually uniform pressure stress field whoseextremely high value, optionally reaching or exceeding 100 MPa,corresponds to the internal pressure, while deformations and shearstress remain quite low.

In the case of the example illustrated, the circumferential pressure orhoop stress resistance is substantially assured by the saidpressure-absorbing armor cladding (10) consisting of a closely coiledwire or strip, preferably of the interlocking wire type such as Zetawire, while the axial components of the force are retained by the pairof armor sleeves (11a, 11b) consisting of a plurality of wires atopposing angles of, for instance, 30° or 40°, in relation to each other.Alternatively, resistance to the internal pressure can be provided by asingle pair of armor sleeves whose wires are wound in opposite directionto each other at an angle of about 55°. The wires of the armor sleeves(10, 11) typically consist of metal such as steel or aluminum, or of apreferably fiber-reinforced plastic, or even of a high-strength fibermaterial.

The flexible tubular conduit is protected by an outer sheath (12)preferably made by extrusion from a thermoplastic polymer.

The role of the flexible metal pipe (1) is to assure crush resistance ofthe flexible conduit and to prevent a collapsing of sealing sheath undercertain operating conditions.

Compared to bonded flexible pipes, the flexible conduit (2) is of theunbonded flexible type that incorporates separate structural elementswhich is a particularly interesting aspect of this invention.

In the case of the example per FIG. 3, the elastomer layer (8)constitutes a continuous tubular sleeve which envelops the flexiblemetal pipe (1), and its outer surface, which is in contact with theinner surface of the sealing sheath (9), is approximately cylindrical,with a minor depression (18) at the location of the interstitial spaces(5). The elastomer of the layer (8) fills the interstitial spaces (5) inessentially complete fashion. Alternatively, depending especially on theviscosity and the amount of the elastomer as well as the fabricationprocess, it would be possible according to a mode of implementation notillustrated, to produce the intermediate layer (8) with less penetrationin the interstitial spaces (5) corresponding to side a illustrated inFIGS. 3A and 3B.

FIGS. 4 to 6 show an enlarged, partial longitudinal section through aflexible conduit according to a second mode of implementation,incorporating an intermediate elastomer layer (8) consisting of anelastomer tape (8A) placed in the interstitial space (5) which separatesthe cylindrical outer parts (13a, 13b, 13c, . . . ) of the successivehelical turns constituting the flexible metal pipe (1). The alternatingsuccession of cylindrical outer parts (13) of the metal pipe and theouter surfaces (14) of the elastomer tape (8A) produces an approximatelycylindrical surface which supports the sealing polymer sheath (9) incontinuous fashion.

When the flexible metal pipe is made up of a continuous helical coil ofa single strip such as an interlocking hoop-type strip (3), theelastomer layer (2) is comprised of a single continuous tape (8A).Alternatively, the flexible metal pipe can incorporate one or severalcontoured sections coiled in parallel, with the elastomer layer (2)consisting of a number of tapes (8A, 8B, . . . ) equal to the number ofcontoured sections (3A, 3B, . . . ) of the flexible metal pipe.

FIG. 4 which illustrates a variation of the second mode ofimplementation also shows the armor cladding of the flexible pipe,incorporating in this case a pressure shield (10) and twotension-absorbing sleeves (11a, 11b) as well as the outer sheath (12).

In the case of the variations according to FIGS. 4 and 5 the elastomerpartially penetrates into the interstitial spaces (5), with the innerend of the area occupied by the elastomer located at a radial distanceof a relative to the cylindrical surface defined by the outercylindrical parts (13) of the flexible metal pipe. The version accordingto FIG. 6 incorporates an intermediate layer consisting of an elastomertape penetrating the interstitial spaces (5) in approximately completefashion.

As compared to the ideal configuration which would be a perfectlycylindrical surface along the extension of the cylindrical sections (13)of the interlocked strip, the outer surface (14) of the elastomer maydisplay an irregular form such as a minor depression or bulge.

The irregularity in the outer surface (14) would preferably be in theform of a hollow like a meniscus whose concave side faces toward theoutside as illustrated in FIGS. 4 and 6. In this case, the polymersealing sheath (9) exhibits on its inner side a slight bulge (15) whosethickness d in the radial direction relative to the cylindricalreference surface defined by the cylindrical surfaces (13) of theinterlocked strip is preferably less than or equal to 0.3 e, e being thethickness of the sheath (9) in its cylindrical section around thesurfaces (13).

Alternatively, the elastomer tape (8A) can be of a shape that isslightly convex toward the outside (FIG. 5). Its outer surface (14) hasa cylindrical central part which connects to the outer surface of theinterlocking strip (3) in a gradual progression with a very slightcurvature and which is marginally separated from the said cylindricalreference surface, with the radial distance separating the two surfacespreferably being less than 0.2 e.

In general, regardless of the mode of implementation chosen and inparticular in the case of the examples shown in FIGS. 1 to 6, goodresults are achieved if the curvature of the inner surface of thepolymer sealing sheath (9) remains limited to very low levels in theareas adjoining interstitial spaces (5) where it can have minorirregularities. Preferably, the smallest radius of curvature that thisinner surface should display is greater than 0.5 e and, better yet,greater than the e-value of the thickness of the sheath (9), with theseradii of curvature at least equal to 2 e permitting maximum utilizationof the intrinsic properties of the material.

The thickness of the shrinkable polymer sheath (9) may generally varybetween 1 and 30 mm and the average would be between 3 and 15 mmdepending primarily on the diameter of the flexible tubular conduit.

The width l of the interstitial space (5) at the plane of its outeropening, i.e. its width between the cylindrical parts (13) ofneighboring helical turns, may vary between 2 and 40 mm. The edges ofthe interlocked contoured section, such as the interlocked strip (3),which form the boundaries of the space (5) are preferably rounded sothat the width of the interstitial space diminishes from the outsidetoward the inside. If measured at a plane corresponding to the mid-pointof the radial depth h of the interstitial space, the width of the spacemay be on the order of 1 to 15 mm. In practice, the depth h of the spacemay vary between 1.5 and 30 mm, meaning that the h/l ratio between thedepth h and the outer width l may thus vary between 0.4 and 1.4.

The fabrication of substantial continuous lengths of the flexibleconduit according to this invention can be accomplished producing thepolymer sheath (9) by conventional extrusion methods. Where theelastomer layer (8) constitutes a continuous tubular envelope around theflexible metal pipe, the elastomer can be applied by extrusion onto theflexible metal pipe. In this case it is possible for instance tosimultaneously coextrude the shrinkable polymer and the elastomer bymeans of two extruders and a double-headed flow-distribution box inwhich the flexible pipe to be sheathed is centered. The penetration ofthe elastomer into the interstitial spaces (5) between the helices ofthe flexible metal pipe now depends, especially in a first pass, on theviscosity of the thermoplastic elastomer in its molten state. It is alsopossible to sheathe the flexible metal pipe conventionally by extrudingthe elastomer sheath onto the metal pipe and then cover the assemblywith a shrinkable polymer layer in a second, in-line extruding operationfurther downstream at the output end of the first extruder from whichthe elastomer-coated flexible pipe emerges (extrusion tandem), or in aseparate extruding operation performed after the first extrusion, oreven by sheathing the flexible metal pipe with the elastomer, optionallydissolved in a solvent and then, after perhaps a reticulation and/orevaporation of the solvent, in a second pass, covering the assembly witha layer of shrinkable polymer by extrusion sheathing.

Alternatively, the intermediate elastomer layer can be produced eitherin the form of a continuous tubular sleeve as illustrated in FIG. 3, orin the form of a tape (SA) placed in the interstitial spaces (5), asshown in FIGS. 4 to 6, by an induction process, or by spraying forinstance with an aerosol or especially electrostatic precipitation, orby immersion in a liquid bath involving for instance the dissolving ofthe elastomer in a solvent, or in a fluidized bed, or by any other knownprocess for covering the surface and/or the interstitial surface gaps ofthe flexible metal pipe with the elastomer. In the case of vulcanizableelastomers, the elastomer can also be successively applied to the metalpipe in its raw state and then vulcanized, preferably prior to theextrusion of the sealing sheath (9). One advantageous process involvesthe application of the elastomer by passing the flexible metal pipe incontinuous fashion through a chamber filled with raw elastomer, forwhich the metal pipe (1) enters and exits the chamber through circularopenings which may be provided for instance with a rubber collar whosediameter is calibrated in a way that it embraces the pipe (1) or,leaving a certain amount of free space, that the intermediate elastomerlayer can be produced in the form of a tape (8A) applied in theinterstitial spaces or in the form of a continuous tubular sleeve.

According to another application process, the elastomer can be put inplace by helically wrapping it around in the form either of ties or of acontinuous tape, the elastomer being in the vulcanized or thermoplasticstate. One can also use tie rings if the material is sufficiently softto permit adaptation to the desired shape of the elastomer tape (8A).One would preferably use a ring or tie in the form of an elastomer whosecross section is so made as to correspond to the configuration of theinterlocking contoured sections (3) which radially flank and delimit theinterstitial space (5) on each side. Ties so shaped, having a crosssection corresponding to the profile of the interstitial spaces, canthus constitute for instance the tape (8A) illustrated in FIG. 3.

Without departing from the framework of this invention, one can producean intermediate elastomer layer (8) in the form of a continuous tubularsleeve by helically coiling an elastomer ribbon with the edges butting,with the elastomer being sufficiently soft to permit easy shapingespecially under the effect of the extrusion of the sealing sheath (9),so as to produce a regular, fairly smooth outer surface withoutoverlapping and without gaps between adjoining turns. On its innersurface the band may incorporate a raised midsection that protrudes inadaptation to the profile of the interstitial spaces (5) so as tosecurely fill the spaces to a certain depth corresponding to the sidewall a per FIGS. 4 and 5.

A variation of this invention, not illustrated, consists in theinterpositioning of a thin sheet produced by wrapping one or severallayers of a tape, made for instance of a fabric, of fibers or of aplastic material optionally fiber-reinforced, between the flexible metalpipe (1) and the intermediate elastomer layer (8). For easier industrialproduction, the wrapping of the tape may take place by the overlaying ofa sheet of regular characteristics; the elastomer material supportingthe tape is not in contact with the surface of the flexible pipe and istherefore not affected and/or degraded by the surface irregularitiescreated by such overlaying. One uses preferably a tape of sufficientmechanical strength so that the sheet permits easy partial and regularfilling of the interstitial spaces (5) with the elastomer of theintermediate layer.

Within the framework of this invention, and for the purpose ofstrengthening the adhesion between the elastomer and the shrinkablepolymer, a certain amount of shrinkable polymer can be added to theintermediate elastomer layer and/or a certain amount of elastomer can beadded to the shrinkable polymer prior to their extrusion for instance byone or the other of the methods described above. One can also interposebetween the intermediate elastomer layer and the shrinkable polymersheath a layer consisting of a mixture of elastomer and shrinkablepolymer, which can be accomplished for instance by coextruding athree-layer sheath of elastomer/elastomer+shrinkable polymer/shrinkablepolymer.

The thickness of the intermediate elastomer layer or the TPE maygenerally vary between 0.1 and 2 mm measured from the apex of theflexible conduit.

The thickness of the shrinkable polymer sheath (9) may generally varybetween 1 and 30 mm and is usually between 3 and 15 mm dependingprimarily on the diameter of the flexible tubular conduit.

Oil and gas production

The flexible tubular conduit that is the object of this invention isespecially suitable for use in oil and gas exploration/extraction wherethe inner diameter of the flexible metal pipe may be on the order of 20to 600 mm and more typically between 50 and 400 mm, with the internalpressure in the conduit typically being greater than 1,450 psi and,depending on the diameter, can reach or exceed 7,250 psi or even 14,500psi. Such flexible pipes are particularly well suited for use involvinghigh temperatures which, depending on the polymers chosen, may reach orexceed values on the order of 100° C. to 120° C. which constitutes thelimits currently possible.

EXAMPLES

The following examples illustrate this invention without being in anyway limiting in nature.

Around a flexible steel pipe 32 mm (11/4") in diameter and made up ofhelical turns, or helices, between which there are hollows andinterstitial spaces to permit articulated bending, an elastomer layer(8) constituting a continuous tubular envelope or sleeve around themetal pipe is applied by the method indicated in each of the tablesrelating to each of the examples given, and a semicrystalline polymerlayer is extruded or coextruded as indicated in the tables. For purposesof comparison, the same pipe is produced under the same conditions withthe same semicrystalline polymer sheath, but without the intermediateelastomer layer.

The pipes are tested in the following manner:

The sheathed pipe is placed on two stationary supports. Using a bendingwheel with a radius of 75 mm (3"), pressure is exerted at a pointequidistant from the two pipe supports. A pressure of 725 psi isapplied. The pipe bends around the wheel. The indentation depth of thewheel indicates the ability of the flexible pipe to deform.

In all the examples the Shore A and D hardness values are measuredaccording to ISO standard 868.

Example 1

In all the tests of Examples 1-4, the semicrystalline polymer ispolypropylene (PP) with a melt index of 3 g/mm as measured according toISO 1133, and a thickness of 5 mm (1.8"). (APPRYL®3030 FN1 by the APPRYLCo.).

The elastomer is:

* Polyurethane polyether (UTAFLEX® TB 1 by the UETWILLER Co.) - Shore Ahardness=50 after reticulation.

** Copolymer of polyamide and polyether units combined by esterfunctions, PEBAX® 2355 ELF ATOCHEM - Shore A hardness=75; bendingmodulus at 23° C.=15 MPa as measured according to ISO standard 178.

*** Polymer VF₂ -C₂ F₃ Cl in a molar 50/50 proportion, having a bendingmodulus at 23° C. of 250 MPa measured by ISO standard 178.

    ______________________________________                                        Test temperature: 0° C.                                                                           Thickness, measured                                Elastomer                  from apex of the                                   layer     Application method                                                                             helices                                            ______________________________________                                        Polyurethane*                                                                           By induction followed by                                                                       0.5      mm                                        2 components                                                                            baking for 1 hour at 80° C.                                  Polyether-                                                                              Elastomer extrusion onto                                                                       1        mm                                        esteramide**                                                                            the pipe followed by                                                          extrusion of the PP                                                 Polymer***                                                                              Direct coextrusion of PP                                                                       1        mm                                        VF.sub.2 -VF.sub.3                                                                      onto the steel pipe                                                 ______________________________________                                    

The above test results show better deformability, and in particularbetter bending ability, of the flexible pipes sheathed with anintermediate elastomer layer sandwiched between the so-called skeletonor frame of the flexible steel pipe and the outer shrinkable polymersheath (according to this invention).

Example 2

In all of these cases, the elastomer is a polyester polyurethane havinga Shore A hardness of 88 (ESTANE® 58271) and a thickness of theelastomer layer of 1.5 mm measured from the apex of the helices.

    ______________________________________                                        Test temperature: 0° C.                                                Semicrystalline polymer                                                       constituting the sealing                                                      sheath        Application method                                                                             Thickness                                      ______________________________________                                        Polyethylene  By extrusion onto the pipe                                                                     5 mm                                           (Mn˜10.sup.5                                                                          extrusion-coated with                                                         elastomer                                                       Polyamide-11* Coextrusion onto the metal                                                                     4 mm                                           (RILSAN BESNO TL                                                                            pipe                                                            Copolymer     Extrusion onto the metal                                                                       5 mm                                           ethylene/TFE**                                                                              pipe extrusion-coated with                                      (TEFZEL 200 by                                                                              elastomer                                                       DUPONT                                                                        ______________________________________                                         *40,000 ≦ MN ≦ 45,000                                           **Shore D = 75, impact resistance at -55° C. = 187 J/m measured        according to                                                             

ASTM D 256.

The above test results show improved deformability, and in particularbetter bending ability of the flexible pipes which are sheathed with anintermediate elastomer layer sandwiched between the frame of theflexible steel pipe and the outer shrinkable polymer sheath (accordingto this invention).

Example 3

Around a flexible steel pipe 32 mm (11/4") in diameter and made up ofhelices between which there are hollows and interstitial spaces topermit articulated bending, the following sheathing is applied bysuccessive extrusions: A layer of polyester polyurethane (ESTANE® 58271)0.5 mm (0.02") thick from the apex of the helices, and then a vinylidenepolyfluoride layer FORAFLON® 1000 HD) (sample 1), 5 mm (0.2") thick. Thepolyester polyurethane has a Shore A hardness of 88 and displays aviscosity reduction of more than 70% over 30 days at 120° C.

For comparison purposes the same pipe is produced under the sameconditions, except without the intermediate polyurethane layer (sample2).

The two pipes are compared under the conditions shown below.

The sheathed pipe is placed on two stationary supports. Using a bendingwheel having a radius of 75 mm (3"), pressure is exerted at a pointequidistant from the two pipe supports. A pressure of 725 psi isapplied. The pipe bends around the wheel. The indentation depth of thewheel indicates the deformability of the flexible pipe. The maximumheight is 170 mm (6.7"); it corresponds to the perfect circumflexion ofthe pipe over the radius of curvature of the wheel. If during theindentation process the flexible pipe ruptures, the depth is noted. Thegreater the depth, the greater the bending ability of the pipe.

    ______________________________________                                                     Indentation Depth                                                Temperature    Sample 1     Sample 2                                          ______________________________________                                        20° C.  170 mm       120 mm                                                           No rupture   Rupture                                           -30° C. Rupture at   Rupture at                                                       150 mm       80 mm                                             ______________________________________                                    

Example 4

The samples 3 and 4 are prepared in the same manner as samples 1 and 2except that the vinylidene polyfluoride is plasticized, at 7.5% byweight, with N-butylbenzene sulfonamide.

Sample 3 has an intermediate layer of polyester polyurethane 1 mm(0.04") thick above the apices of the helices, and an outer layer, 6 mm(0.24") thick, of plasticized vinylidene polyfluoride.

Sample 4 does not have an intermediate polyester polyurethane layer.

Successive bending tests of the sheathed pipes are performed on amandrel having a radius of 68 mm (2.7"). After each new bending test,the pipes are subjected to a temperature of -10° C. for one hour.

Sample 3 could be bent five times without rupturing.

Sample 4 whitens after the fourth bending and splits at the fifth.

The sample pipes 3 and 4 are aged for one month at 150° C. in aventilated oven.

The same bending test is then performed at -10° C.

Sample 3 whitens at the third bending and cracks at the fourth.

Sample 4 breaks at the first bending.

What is claimed is:
 1. A flexible metal pipe whose outer surface has interstitial spaces (5), said pipe being covered with a sealing sheath of shrinkable polymer (9), wherein an elastomer layer (8) is provided intermediate between the shrinkable polymer sheath and the metal pipe, said intermediate elastomer layer being in the form either of a continuous tubular envelope or of a tape, and said intermediate elastomer layer being positioned in said interstitial spaces.
 2. A flexible metal pipe according to claim 1 comprising interior and exterior metal walls and being arranged with one or more turns having one or more apexes, said pipe being sheathed with a poly(vinylidene fluoride) layer and a polyurethane thermoplastic elastomer layer, said polyurethane layer being interposed in an intermediate position between the external metal wall of the pipe and the poly(vinylidene fluoride) layer.
 3. A pipe according to claim 2 whose polyurethane thermoplastic elastomer layer has a Shore A hardness of less than
 92. 4. A pipe according to claim 2 whose polyurethane thermoplastic elastomer layer undergoes a reduction in viscosity of at least 60% after 30 days at 120° C.
 5. A pipe according to claim 3 whose polyurethane thermoplastic elastomer layer undergoes a reduction in viscosity of at least 60% after 30 days at 120° C.
 6. A pipe according to claim 2 whose polyurethane thermoplastic elastomer has a viscosity at 200° C. within the following limits:

    ______________________________________                                         Corrected shear rate s.sup.-1                                                                  Viscosity in kPa.s                                             ______________________________________                                          4.09           0.7-1.3                                                        13.64           0.25-0.85                                                      36.15           0.19-0.78                                                      122.91          0.12-0.70                                                      ______________________________________                                    


7. A pipe according to claim 3 whose polyurethane thermoplastic elastomer has a viscosity at 200° C. within the following limits:

    ______________________________________                                         Corrected shear rate s.sup.-1                                                                  Viscosity in kPa.s                                             ______________________________________                                          4.09           0.7-1.3                                                        13.64           0.25-0.85                                                      36.15           0.19-0.78                                                      122.91          0.12-0.70                                                      ______________________________________                                    


8. A pipe according to claim 4 whose polyurethane thermoplastic elastomer has a viscosity at 200° C. within the following limits:

    ______________________________________                                         Corrected shear rate s.sup.-1                                                                  Viscosity in kPa.s                                             ______________________________________                                          4.09          0.7-1.3                                                         13.64          0.25-0.85                                                       36.15          0.19-0.78                                                       122.91         0.12-0.70                                                       ______________________________________                                    


9. A pipe according to claim 5 whose polyurethane thermoplastic elastomer has a viscosity at 200° C. within the following limits:

    ______________________________________                                         Corrected shear rate s.sup.-1                                                                  Viscosity in kPa.s                                             ______________________________________                                          4.09          0.7-1.3                                                         13.64          0.25-0.85                                                       36.15          0.19-0.78                                                       122.91         0.12-0.70                                                       ______________________________________                                    


10. A pipe according to claim 2 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 11. A pipe according to claim 3 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 12. A pipe according to claim 4 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 13. A pipe according to claim 5 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 14. A pipe according to claim 6 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 15. A pipe according to claim 7 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 16. A pipe according to claim 8 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 17. A pipe according to claim 9 whose intermediate polyurethane thermoplastic elastomer layer has a thickness of 0.1 to 2 mm from the apex of the flexible metal pipe.
 18. A flexible pipe consisting essentially of interior and exterior steel walls, said pipe being sheathed with a poly(vinylidene fluoride) layer and a polyurethane thermoplastic elastomer layer, said polyurethane layer being interposed in an intermediate position between the external steel wall of the pipe and the poly(vinylidene fluoride) layer.
 19. A flexible pipe according to claim 18 wherein said steel pipe has an internal diameter of from 20 to 400 millimeters, said intermediate polyurethane layer has a thickness of from 0.1 to 2 millimeters, and said poly(vinylidene fluoride) sheathing layer has a thickness of from 1 to 10 millimeters.
 20. A flexible pipe according to claim 18 which further comprises a polyurethane layer coated on the internal steel wall of the pipe.
 21. A flexible metal pipe whose outer surface has interstitial spaces (5), said pipe being covered with a sealing sheath of shrinkable polymer, wherein an elastomer layer (8) is provided, in the form of either a continuous tubular envelope or a tape positioned in the interstitial spaces (5), intermediate between the shrinkable polymer sheath and the metal pipe, provided that when the shrinkable polymer sheath is composed of poly(vinylidene fluoride), the elastomer layer is not polyurethane.
 22. The flexible pipe of claim 21 wherein the shrinkable polymer is a semicrystalline polymer and wherein the elastomer is selected from the group consisting of vulcanized elastomer, reticulated elastomer, thermoplastic elastomer, and mixtures thereof.
 23. The flexible pipe of claim 21 wherein the degree of stiffness of the elastomer is less than that of the shrinkable polymer.
 24. The flexible pipe of claim 21 wherein the elastomer is selected from the group consisting of silicone elastomers, polyamide thermoplastic elastomers, thermoplastic polyurethanes, ethylene/propylene/diene monomer copolymers, acrylonitrile/butadiene/styrene copolymers, styrene/butadiene/styrene copolymers, methyl methacrylate/butadiene/styrene copolymers, ethylene/carbon monoxide copolymers, ethylene/carbon monoxide/vinyl acetate terpolymers, acrylic rubbers, thermoplastic polyolefins, polyester thermoplastic elastomers, ethylene/ethyl acrylate, ethylene/ethyl acetate, and ethylene/vinyl acetate copolymers and terpolymers, fluorinated elastomers, and mixtures thereof.
 25. The flexible pipe of claim 21 wherein the shrinkable polymer is selected from the group consisting of polyolefins, polyamides, polyurethanes, polyureas, polyesters, polyethers, polyoxides, polysulfides, polyether-ether-ketones, copolymers of the preceeding, homopolymers and copolymers of vinylidene fluoride ("VF₂ "), homopolymers and copolymers of trifluoroethylene ("VF₃ "), copolymers and terpolymers comprising two or more different members selected from the group consisting of VF₂, VF₃, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropene, and ethylene, said shrinkable polymers being used by themselves or mixed with other polymers in which mixtures said shrinkable polymers are present in amounts of at least 70% by weight.
 26. A flexible tubular conduit suitable for moving liquids under high pressure or at high temperatures incorporating a sheathed pipe according to claim
 1. 27. The flexible tubular conduit of claim 26 further comprising armor cladding.
 28. A method for the production of off-shore oil or gas which comprises transporting said oil or gas from below the floor of the ocean to the surface of the ocean in a flexible tubular conduit according to claim
 1. 29. A flexible metal pipe comprising interior and exterior metal walls and being arranged with one or more turns having one or more apexes, said pipe being sheathed with a poly(vinylidene fluoride) layer and a polyurethane thermoplastic elastomer layer, said polyurethane layer being interposed in an intermediate position between the external metal wall of the pipe and the poly(vinylidene fluoride) layer. 